1. Field of the Invention
The present invention concerns the field of orthodontics. More specifically, the present invention relates to a method and tools for positioning brackets on teeth of a patient.
2. Discussion of Background Information
In orthodontics one aim for moving teeth of a patient into appropriate positions such that the teeth can fulfill their function optimally, and such that an aesthetically pleasing appearance of the teeth is achieved. For moving teeth within a patient's mouth, an orthodontist may use so-called aligners which essentially represent negative models of the patient's teeth. Alternatively a set of braces or orthodontic brackets may be used, wherein a bracket is positioned on and attached to each tooth of a patient, and a rectangular metal arc wire is mounted into the slot openings of the brackets for engaging the forces rendering the teeth to move into the desired positions.
The orthodontic brackets may be positioned directly on the teeth within the patient's mouth. As the form and position of each bracket determines the movement of the tooth said bracket is attached to, it is apparent that an accurate positioning of each of the brackets on the patient's teeth is important for achieving the desired movements. However, accurate direct positioning of brackets on the teeth of a patient inside the patient's mouth is a difficult task.
For improving accuracy of directly positioning brackets on the teeth it is known to utilize jigs. For example US 2007/0031775 A1 teaches a placement jig for locating an orthodontic appliance on a tooth. The placement jig is provided with a cavity formed in the jig body and conforming the contour of an occlusal portion of a tooth crown, which cavity is coated with a releasable adhesive to hold the jig to the tooth as the orthodontic appliance is bonded to the tooth. A connecting structure is fixed to the jig body, and appliance receiving structures are machined on each jig body during the jig's manufacturing.
For further improving the accuracy of bracket positioning, “indirect” methods have been developed, wherein the brackets are positioned on a three-dimensional positive tooth model of the patient's teeth outside the patient's mouth rather than directly on a tooth within the patient's mouth. Positioning the brackets on a positive tooth model improves visualization and permits using measuring devices for more precisely determining the position of the brackets. When the brackets are positioned on and releasably bonded to the teeth of the positive tooth model, a transfer tray is fabricated and used for transferring the brackets from the positive tooth model to the patient's mouth. U.S. Pat. Nos. 4,952,142 and 5,971,754 disclose variations of indirect positioning methods.
However, there are drawbacks in these conventional bracket positioning systems and methods. Typical brackets comprise a broad flat base for attaching the bracket to the tooth, and structures protruding from the base thereby forming a rectangular slot for receiving an arc wire. Typical brackets also comprise structures called “tie-wings” which are used to anchor a disposable ligature. Because of the necessity of these structural elements, the brackets must possess a certain degree of structural profile height and shape irregularity. The structural profile and shape irregularity render it difficult to remove the transfer tray from the patient's teeth once the brackets have been transferred from the positive tooth model and bonded to the patient's teeth, in particular because the transfer tray is form-fitting the brackets for securely holding the brackets in place during their transfer to the patient's mouth.
Hence, there is a desire for improving the method of indirect positioning of brackets, and it is an object of the present invention to provide an improved method for indirect positioning of brackets.
The object is achieved by a method of indirect positioning brackets utilizing a positive tooth model, using said positive tooth model for manufacturing a transfer tray for accommodating at least one bracket, and using said transfer tray for positioning and adhering the at least one bracket onto the patient's tooth or teeth.